What does the term 'lag' refer to in instrument flying?

In instrument flying, the term 'lag' specifically refers to the delay in reaching stable instrument indications. When a pilot makes a control input to change the aircraft's attitude or flight path, there is often a brief period where the instruments do not reflect the new condition immediately due to the inherent physical response of the aircraft and the measuring instruments. This lag can be attributed to the time it takes for the aircraft to respond to control inputs and for instruments to stabilize at their new readings.

Understanding this concept is vital for instrument pilots, as it highlights the importance of anticipating changes in aircraft behavior and reading instruments with an awareness of this delay. Pilots must be cautious of this lag, especially during critical flight phases such as climbs, descents, or turns, as it can lead to inappropriate reactions if the pilot does not account for the time lag. Thus, accurate interpretation of instrument data requires recognizing that there may be a transient phase between the actual conditions and what the instruments display.